Environmental isotopes and movements of sulphurated water in Latium, Italy

The isotopic composition of six sulphur-containing springs in Latium was analysed continuously. These springs represent the emergences of free aquifers charged by precipitations collected on karstified and fissured calcareous and calcaro-dolomitic reliefs. The heavy-isotope content of the precipitations was measured at a number of stations at different altitudes on the Tyrrhenian and the Adriatic sides. The isotopic composition gradients vary widely with the seasons and the reconstitution of the 'isotopic charging areas' requires an examination of the infiltration conditions. In the present case practically all the precipitations participate in recharging. The variations in isotopic composition of the water are interpreted as dilutions between recent shallow groundwater and deep well-homogenized groundwater. In general the surface contributions are less than 10% except for the small Lavinio spring, where close on two thirds of the water is recent, and the Acquasanta emergence, where the comparative pattern of salt and 18O content suggests that the reservoir has a complex mechanism of operation. The dissolved salt, tritium and 14C content is compatible with this theory. The 34S content of the associated sulphides and sulphates indicates a mixture of two reserves of sulphur, one being deep perivolcanic sulphur and the other sulphur from evaporitic permotriassic sediments. In addition, sulphides and sulphates are linked by an oxidoreduction mechanism. The 18O content of the sulphates shows the same characteristics. The results as a whole are in agreement with the conclusions reached by analysing the salt and 18O content of the water circuits. (author)